Apparatus for measuring backlash in gears



eco 8, 953 A. l. BEAN 2,661,542

APPARATUS FOR MEASURING BACKLASH IN GEARS Filed April 4, 1946 4 Sheets-Sheet l Dec. 1953 A. l. BEAN APPARATUS FOR MEASURING BACKLASH IN GEARS Filed April 4, 1946 I265 02" iizz/jiawz M D@. 1953 A. l. BEAN APPARATUS FOR MEASURING BACKLASH IN GEARS Filed April 4, 1946 4 Sheets-Sheet 3 es. 3, 1953 A. l. BEAN 2,661,542

APPARATUS FOR MEASURING BACKLASH IN GEARS Filed April 4, 1946 4 SheetsSheet 4 Patented Dec. 8, 1953 UNITED STATES PATENT OFFICE APPARATUS FOR MEASURING BAGKLASH IN GEARS Application April 4, 1946, Serial No. 659,524

9 Claims.

The object of this invention is to provide a simple and accurate apparatus for determining whether or not th backlash of gears produced for any purpose is within prescribed limits of tolerance, and also for measuring to close limits of accuracy the actual backlash of any particular gear.

Devices or apparatus in which this invention is embodied are based on the principle that the distance between the centers of meshing gears is greater or less according as the backlash of either gear or both gears is greater or less, and that the pressure angle of the gear teeth is a factor which governs the difference of center dis tance between gears having no backlash and those having a given amount of backlash.

In putting this invention into practice I have utilized means for mounting a test gear in mesh with a master gear with provisions for movement of one gear toward and away from the other and a measuring or indicating means operable in consequence of such relative movement through transmission means adjustabl to conform with the pressure angle of the test gear.

The invention is explained in the following specification with reference to concrete embodiments shown in the accompanying drawings, in which Fig. 1 is a plan view of a measuring apparatus showing one embodiment of the invention;

Fig. 2 i a front elevation of the apparatus shown in Fig. 1, omitting the base by which the parts thereof are supported;

Fig. 3 is a detail sectional view taken on line 3-3 of Fig. 1 shown on an enlarged scale;

Fig. l is a transverse sectional View taken on line -ii of Fig.3;

Figs. 5-l3 inclusive are diagrammatic views showing the principles according to which the desired results ar obtained by the use of this apparatus;

Fig. 14 is a plan view of a modified form of measuring machine embodying the same principles;

Fig. 15 is a sectional view taken on line iii-I5 of Fig. 14.

Like reference characters designate the same parts wherever they occur in all the figures.

The machine shown in Figs. 1-4 has a base I which supports a fixture 2 carrying a stud 3 on which the gear to be tested is mounted rotatably. Such a gear is here designated by the letter W.

The base supports also a holder i carrying a pivot stud 5 on which a master gear 5 may be mounted rotatably in mesh with the gear to be tested. The holder 4 is mounted to turn on a pivot stud 71 held by a carriage 8, which is adjustable on the base I to move in directions toward and away from the fixture 2. By means of such adjustment the master gear can be brought into mesh with test gears of different diameters. Also the fixture 2 can be removed and substituted by other fixtures for holding various types of gear, internal as well as external gears.

The-re is mounted on the end of the holder 4 remote from the pivot i, that is, at the opposite side of the master gear pivot from the holder pivot, a bracket ii having bearings ill and I i (Fig. 3), in which a shaft E2 is rotatably mounted. This shaft has a cam face 53 which, due to the long distance at which it is situated from pivot I, is approximately fiat; but it may be curved suitably to compensate for its arcuate path, in transmitting motion to indicating means later described. The shaft also carries an indicator arm or index it overlying the upper surface of the bracket 9 and serving in conjunction with an angle scale "5 on the top of the bracket, to incline the face It at definite prescribed inclinations to the common plane of the pivot '17 and shaft HE. A set screw ll is mounted in the side of bracket 9 in position to bear on the shaft l2 and secure it in any position of angular adjustment.

Shaft i2 is called for th purpose of this description the conversion shaft. It is made angularly adjustable to correspond with the pressure angles of different test gears, and preferably the graduations it are designated by numerals or other symbols to indicate pressure angles for which the conversion shaft may be adjusted.

Mounted on the carriage 8 is a micrometer indicator it having a pointer is movable rotatably over a graduated dial 2@, shown in Fig. 1, and a plunger 2i, movable endwise through a guide sleeve 22, which operates multiplying mechanism in the casing of the indicator to impart movement to the pointer it. The instrument here shown is one of a well known and commonly used type in which movement of the plunger is multiplied by a factor of 150 at the extremity of the pointer. The dial 2% is mounted on the casing of the instrument by a bezel 23 whereby the dial can be turned independently around the axis of the pointer I9. There are also adjustable stationary pointers 2t and 25 rotatable around the axis of the pointer is, the purpose of which is to indicate tolerance limits for movements of the pointer 19.

Guide sleeve 22 is secured to the side of the indicator casing. A bracket 26 is secured to this sleeve and supports a bell crank lever 21, of which one arm extremity 28 i located to bear on the cam face i3 of the conversion shaft and the other arm extremity 29 is located to bear on the end of plunger 25. A spring in the indicator casing acts on the plunger 24 tending to, holditiatfthe outer limit of its movement. This spring keepsthe plunger in contact with the bell crank lever 2'5 and the latter in contact with the conversionshaft 2.

cooperate with a screw 3! to exert pressure on the holder either toward or'aawa-y fromythe test gear according to adjustments-'of the-screw;

For testing external gears, the spring means are set to exert force on the gear dtowardqthe-test.

gear (to the left with respect to these drawings) and when an internal gear is to be teste'd,-- the spring mean are set to exert force in the opposite direction. I

In order to test a gear for backlash,an accuratemaster gear is mounted-on the pivot?) of the holder 4, a master gear having. the: same diam eter 'andpitch as the gears .to'be tested and hav inga known backlash ismounted on the work holder fixture 2, the carriage 8 is advanced to bring the master gears into mesh and put the holder 4 in an intermediate .position:from which it can be moved in one direction against the pressure of'the spring. means 3B, and in the opposite directicnby the spring, a distance in either direction greater. than. the permissible backlash of the gears to be tested, the conversion shaft isrset with the index markof it pointer is in.

register with that one of the; graduations It which corresponds to the pressure-angle of such. gears, the dial 2c of the indicator is turned so that the graduation thereon .whichdesignatesthe known-backlashof the master work. gear. registers with the pointer 19,; and the tolerance pointers 24' and 25. are setto the graduations of thedial which designate --the tolerable limits ofbacklash. Then the -master work-gear. is re moved from the fixture -2,the gear W to-betested iswmountcd on the fixture in; mesh with the master. gear 6, the gears are-rotated and :the movements ofv the pointer l9 are noted.

The instrument now being described issdesigned to permit measurement: of backlash. by directreading on the indicator dial 263., withoutv applying any correction factor, wherefore the conversion shaft I2 is so-locatedthatthe. intersection of the cam face 13 with a selected radius from the holder pivot i is at twice-the distance of the axis of pivot 5 from the axis of pivot 7 when the conversion shaft is; adjusted to a prescribed angle. Since the backlash of. a gear tooth' is equally divided between opposite :sidesof the tooth, the change of center distance between thetest gear and the mastergear due: to a difference': of backlashis proportionalto'half the backlash, wherefore: the factor of '2 applied "to the movementof the conversion shaft due to the ratio between the distances of the cam face of this shaft and the master gear centerfrom the holder pivot, causes the displacement oi=the conversion proportioned and. located that they transmit 10 The spring means 30;, shown by d.otte.d lines in Fig. l, are mounted in the holder s tom master gear 6.

movement to the plunger 2! equal to the displacement of the contact point 28 of the bell crank in the direction perpendicular to the direction of movement of the conversion shaft, within their limited range of movement.

Attention is directed to Figs. 5, 6 and 'l for demonstration .of the principles last described. A tooth t of a test gear having a pressure angle of 20 is shown in Fig. 5 between two teeth of the The full lines and broken lines designating.=the.- master gear teeth represent different positions'of the master gear when meshing with test gear teeth of maximum and minimumbacklash. This designates with exaggera- -tioni-thatthere"may be different amounts of backlash in teeth of the same gear. The dimension-.pdesignatesthe distance measured on the line of action which corresponds to half the e tremedifference of backlash (measured on the pitch circle) and the dimension y designates the shifting..-of the center of the master gear when itrmeshes with the teeth of greatest and least backlash:v Due to thechange of center distance, theline ofaction of the teeth varies between the extremes designated by the lines is and I'd, respectively, and the actual pressure angles vary between the angles designated 0 and 0.

Fig; 6 shows similar conditions with respect to attest gear tooth t having a pressure angle-of 30"; and of which the variation of backlash is the same as in the gear previously described, but the change of center distance y is less, due to the factsthat the pressure angle is greater. The same things are shown by-Fig. with respect to a tooth t -of ale pressure angle gear having the same backlash variation asthegears precedently mentioned. The shift of the master gear center designated y? is greater than in the other cases.

Figs, 8,9 and 10show in'a diagrammatic way, and with exaggeration, the shifting of the master geanholder. about its pivot 1 due to shifting ofv the; master gear centerthrough the distances y. y; and yz with gears. having pressure angles of; 20, 30 characterlii jin 1Flgs.58,1 9 andv 10. designates a planecorresponding to thesurface. i 3 on the conversionrshaft, and thefulland broken lines to which this character is applied indicate, withexaggeration; the extreme positions of the surface [3 occasioned by the rotation of the gears with varying backlash precedently referred to. Figs. 11,;12Qand13 show ona much enlarged scale so much of the diagrams of Figs. ,8, 9 and 10 as are enclosed within the circles 12. A given point on the surface l3 shifts between locations 0 and c' inFig. .11 when the center of the master gear is moved through the distance the same point may shift between locations (1 and d shown in Fig. 12 when the master gear center is moved thedistance y';'anda point on the surface 13 may move between the locations 6 and e when the displacement of the master gear center is the distance 11 The displacements thus indicated correspond to those due to the same amount of backlash in the testgears represented in Figs. 5, 6 and 7. But a follower bearing on the surface I3 and constrained to move in a path perpendicular, or substantially so, to the travel of the conversion shaft (the path of its bearing point being designated 10 in Figs. 11, 12 and 13), is dis placed an equal distance in each instance if the surface [3 is set at an angle to its path of movement equal to the pressure angle of the gear. It is demonstrable mathematically and graphically that with the arrangement and proportions here and 14?, respectively. The reference shown, and with a suitable cam surface I3, the distance by which the plunger of the indicator instrument is moved in consequence of backlash variations, is equal to the amount of backlash.

Instead of using the apparatus to indicate whether or not the backlash of a gear i within permissible limits, the change in center distance between the master gear and test gear can be read directly by setting the parts as follows. A master work gear is mounted on the work holder and meshed with the master gear 6 as previously described, the conversion shaft I2 is turned to incline the cam surface 63, with respect to its directions of movement, at an angle of which the tangent is equal to the ratio between the axial distance of pivot to pivot 5 and the distance from pivot axis l to a prescribed point on face I3, and the indicator dial is turned to bring its zero in register with the pointer [9. The above mentioned adjustment point for the conversion shaft is designated by an indication on the scale [6. Then, when the test gear is substituted for the master work gear on spindle 3, and rotated, the center distance variation is shown and measured directly by the pointer i9 and scale 20.

A variation of the apparatus previously described is shown in Figs. 14 and 15. In this case the pivoted master gear holder 4 is connected with an arm 33 by means of a spring 34, and a fixed distance is maintained between the holder 4 and arm 33, at the points where the spring is connected with them, by a distance rod 35 having conical ends seated in conical sockets in the holder and arm 33. The cone angle of the sockets is larger than the cone angle of the rod ends, whereby a frictionless bearing is provided. The spring is coiled into a helix and has hook ends anchored in sockets 36 and 37 of the holder and arm, respectively. The arm is mounted on the carriage 8 by means of a block 38, secured to the carriage, to which th arm is connected by a leaf spring 39, which is clamped at one end in the block 38 and at the other end in the contiguous end of arm 33. The spring provides a frictionless fulcrum about which the arm 33 can swing pursuant to movements imparted from the holder 4.

An indicator 62 like that previously described. is mounted to slide in a guideway iii in the top wall of the carriage 8 is arranged with its plunger 2! bearing against the contiguous side of the arm Guide-way 43 extends parallel to the surface of 33 on which the plunger bears, and the indicator is held frictionally in the guideway by a clamp ii sliding engagement with a stud :2 which protrudes from the bottom of the indicator casing. 3 is engaged with the head of the and with the clamp dl so as to press the latter against overlying shoulders M at each side of the guideway.

Movement of the indicator along its guideway places the contact point of the plunger at points along the arm 33 variously distant from the fulcrum point of spring 32, whereby the movement imparted to the indicator pointer pursuant to a given displacement of the master gear can be varied in proportion to the pressure angle of the test gear. A scale mounted on the carriage and overlying the plunger guide sleeve 22 bears graduaticns which, by reference to an index mark on the sleeve 22, establishes the location of the indicator at whi h the movement imparted to its plunger will be equal to the backlash of a test gear having a given pressure angle, or proportional to the backlash. In the scale here shown,

the graduations beside which the numerals iii, 20 and 3B are placed show the positions for indicating backlash of gears of 10, 20 and 30 presure angles, respectively. The graduation marked CD designates the position of the indicator for measuring directly displacements of the center of the master gear.

I claim:

1. An apparatus for .ieasuring backlash of gears, comprising holders for a test gear and a master gear, respectively, one of which holders is movable so as to vary the distance between the centers of gears mounted on the respective holders in mesh one with the other, a distance indicator having'a movable plungerand means actuated by said plunger for showing distance measurements, and motion transmission means be tween the movable holder and plunger including a member carried by the movable holder and having a cam surface in pressure transmitting and receiving relation to the plunger, said memher being angularly adjustable to place its cam surface at various inclinations to the path in which the member moves when the holder is displaced.

2. An apparatus for measuring backlash of gears, comprising holders for a test gear and a master gear, respectively, one of which holders is movable so as to vary the distance between the centers of gears mounted on the respective holders in mesh one with the other, a distance indicator having a movable plunger and means actuated by said plunger for showing distance measurements, and motion transmission means comprising a conversion shaft carried adjustably by the movable holder having a cam surface arranged to be set by adjustments of the shaft at varicus inclinationsto the path in which the conversion shaft is moved with movements of the holder, said surface being arranged to impart movement to the plunger in various ratios to the movement of the transmission member according as said surface is variously inclined to the path of its movement.

3. An apparatus for measuring backlash of gears, comprising holders for a test gear and a master gear, respectively, one of which holders is movable so as to vary the distance between the centers of gears mounted on the respective holders in mesh one with the other, a distance indicator having a movable plunger and means actuated by said plunger for showing distance measurements, a transmission element carried by the movable holder having a displacement surface adjustable to various angles to the path in which it travels when the holder is displaced, and a lever having an arm bearing on said surface for displacement thereby in a direction transverse to the before named path and a second arm engaged with the plunger to move the latter when the first arm is so displaced.

4. An apparatus for measuring backlash of gears as claimed in claim 13, wherein said means to vary the ratio of movement transmitted by said lever comprises said indicator being adjustably mounted relative to the lever for locating the point of engagement between the plunger and lever at different distances from the fulcrum of the lever.

5. An apparatus for measuring backlash of gears comprising a base, a fixture on said base having means for supporting a gear rotatably, a carriage mounted on the base to move in directions toward and away from said fixture, a holder pivotally mounted on said carriage having means for-holding; a. gear rotatably with, its; axis at a'distance, from the pivot of the holder and in position for movement toward and away from the gear'holding means of said fixture, said pivotally mounted holder having an outwardly extending portion, a conversion member rotatably mounted on said portion having a cam face adjustable ;by rotation of the member so as to be placed at different inclinations to the path'in which it is movable by angular movement of. the holder, an indicator'mounted on the carriage including relativeiy movable index and scale elements and an actuator therefor, and a lever mounted on the carriage having an arm engaged with said actuator and a second. arm engaged with said' cam face.

6. An apparatus for measuring the backlash of gears, comprising a base, holders on said base for a gear to be measured and a master gear, respectively, one of which holders is movable so as to vary the distance between the centersof gears mounted on their respective holders in mesh one with the other, a backlash measuringjindicator having a movable plunger and means actuated by said plunger for showing backlash measurements, scale carried on base, graduations calibrated on said scale sho .ng the pressure angle of gears to be measured and motion transmission means between said movable holder and plunger adapted to cause movement of the I plunger when the holder is moved, said motion transmission means including a. lever fulcrumed on said base and means cooperating with said scale to vary the ratio of movement transmitted by said lever between said movable holder and said plunger as determined from the pressure .ngle of the gear being measured.

'7. An apparatus for measuring backlash of gears comprising a base, a fixture on said base having means i supporting a gear rotatably, a 4

carriage mounted on the base to move in directions toward and away from said fixture, a holder pivotally mounted on said carriage having means for holding a gear rotatable with its axis at a distance from the pivot of the holder and in.position for movement toward and away from the gear holding means of said fixture; said pivotally mounted holder having a portion which extends to greater distance from its pivot than the dis tance between. such pivot and the axis of the gear supporting means thereof, a scale carried on said base, a backlash measuring indicator mounted on the carriage including relatively movable index and. scale-elements and an actuator for imparting movement to one of said elements, transmission means between said' pivotally mounted holder said actuator, said transmission means including a lever .mounted'on said base independently of saidiholder and an adjustable connection coacting withsaid lever and located between said holder and said actuator to vary the motion transmitting ratio of said lever, said adjustable. connectionbeing so constructed and arranged to cooperate with said scale so as to be variable in accordance with the. pressure angle of the gear to be measured.

8. 'An' apparatus for measuring backlash of gears comprising a base, a fixture onsaid'base having means for supporting a gear rotatably, a carriage mounted on the base to move in directions toward and away from said fixture, a holder pivotally mounted on said carriage having means for holding a gear rotatable with its axis at a .distance: frornthe; pivot: oi the holder and- :in; vposition. for; movement toward and awa y from the. gearholding means ofsaid'fixturasaid pivotallymountedholder having a portion which extendsto a greater, distance from its pivot than the distance between such pivot and the axis of thegear, supporting means thereof, a scale carried on'said base, graduations on said scale showing various pressure angles of gears to be measured, a backlash measuring indicator mounted on the carriage, including relatively movable index and scale. elements, an actuator for imparting 'movement toone-oi: said elements, a .lever having anarm engaged with said actuator toimpart motionthereto 'a-nd'aa second arm in motion receiving relation with the outwardly extending portion of the pivotally mounted holder, and means tovary the, motion transmitting ratio of said-arms'in accordance with the setting of said scale.

9. 1 m apparatus for measuring backlash of gears-comprising a base, a fixture on said base havin *meansfor supporting a gear rotatably, a carriage mounted on the base to move in directions toward and away from said fixture, a holder pivotally mountedon said carriage having means for holding a gear rotatable with its axis at a distance-from the pivotof the holder and in position for movementtoward and away from the gear holding means of said fixture, said ivotally mounted holder having a portion which extends to a greater distance from-its pivot than the distance between such pivot and the axis oi the gear supporting means thereof, a scale carried on saidqbase, graduations calibrated on said scaleto show'plurality of pressure angles, hackl sh measuring indicator mounted on the carriage including-relatively movable index and scale-elements and an actuatorior imparting movement to: cne'ofsaid elements, transmission means between said pivotally mounted holder and said actuatonsaid transmission means including a lever mounted on said-baseindependently of said-holder and an adjustable connection to vary the: ratio of motion transmission of said I lever'betweerr said holder and said actuator, said adjustable connection being constructed and arranged so as to be variable in accordance with the pressure angle of thegear to be measured as determined from the setting of said scale.

ARTHUR I. BEAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,184,399 Wheeler May. 23, 1916 1,222,392 Green et al. Apr. 15, 1917 1,257,483 Hart etal -Feb. 26, 1918 1,390,432 Douglass Sept. 13, 1921 1,554,646 Olson -2 Sept 2, 1925 1,564,589 Laessker Dec..8, 1925 2,190,961 Webber Feb. 25,, 1940 2,447,445 Widen Aug. 17, 1948 FOREIGN PATENTS Number Country Date 555,624 Germany July 25, 1932 608,163 Germany Jan. 13, 1935 OTHER REFERENCES Gages, Gaging 8; Inspection, Hamilton, page 266, The Industrial Press, New York, 1918.

Machinery July 1925, page 888. 

